Below the absolute zero

2013/01/10 Roa Zubia, Guillermo - Elhuyar Zientzia Iturria: Elhuyar aldizkaria

• Fisika

Physicists at the University of Munich have overcome an alleged insurmountable barrier of physics: they cool a gas of potassium atoms at a temperature below absolute zero. To express the temperature they have reached they use negative kelvin. Experts do not agree on whether they have exceeded the limit or acted with the definition of temperature, but there is no doubt that the creator of Munich will open new doors in research.

Lord Kelvin could not reach negative numbers on the Kelvin scale in the 19th century. As investigated in the 20th century. As a matter cools down, energy decreases and in that process energy becomes zero. And Lord Kelvin realized that, tested with any material, this happens at the same temperature, at -273°C. Lord Kelvin called it absolute zero and said it is impossible to get out of that temperature. However, later physicists discovered that in absolute zero the energy of atoms is not zero: quantum mechanics explained that they will always have minimal vibratory energy, the lowest possible energy level.

Lord Kelvin, however, did not study the atoms individually but the gigantic array of atoms or molecules we call gas.Near the absolute zero, most atoms in this group have minimal vibration energy, but there are few at a higher energy level. The temperature measurement of a gas is the mean of the vibration states of all atoms. In short, the relationship between the macroscopic world, gas, and the nanoscopic world, molecules, is complex and has been used by Munich physicists to overcome the insurmountable barrier.

The potassium atoms of the gas have been caught in a network by a laser and have revolutionized the distribution of the energies of the atoms, that is, they have left a few atoms with minimal energy and most have been given a somewhat higher energy. This changes the measurement of the general temperature to move to negative numbers. In addition, a new quantum state has occurred in these captured potassium atoms, which have resulted in very rare physical properties in this “negative temperature”, such as reverse gravity behavior. Researchers claim that they have also seen atoms similar to the dark matter of the universe.

In short, two types of conclusions can be drawn from the results. On the one hand, that the negative value of temperature is only a consequence of quantum tricks, and not that they have actually exceeded the limit of absolute zero down. Lord Kelvin's idea remains correct. On the other hand, the experiment has created or at least allows to create a new state of matter with innovative properties that allow to explore the gases of potassium atoms.